Batteries have transformed electronics, giving us powerful phones, tablets, e-readers, and smart watches. But eventually, every battery runs flat.

Maybe not for long. One startup, RadianX, envisions a world in which portable and edge devices can cut the cord for good without running out of power. The key is a better breed of solar panels.

RadianX has developed a new type of solar material from a family known as perovskites. The material is just as good as existing solar panels outdoors, but twice as good at harvesting light indoors.

“We can harvest any kind of photon, whether it’s an outdoor or indoor photon, and keep the device running longer — or running forever,” Josh Douglas, co-founder and COO, told TechCrunch.

The indoor efficiency of RadianX’s tech could be the key to unlocking what the company calls “edge energy.” Think an e-reader that never needs charging or an IoT sensor that never needs a battery swap. But as with any new category, unexpected uses could emerge, including long-runtime robots or wearables that have been held back by limited battery power.

To fund a commercial-volume production line, RadianX recently raised $5 million in a seed round led by SOSV and Twynam, the company exclusively told TechCrunch. Other investors included One Small Planet, Sachsen Ventures, Avila VC, California Innovation Fund, quantumEDGE, Riceberg Ventures, and Alumni Ventures. Alongside the seed money, Pacific Union Technology Precision Manufacturing is pitching in $4 million of non-dilutive investment to build a dedicated production line for the startup.

It’s not an entirely new idea — solar-powered calculators have been around for decades — but it’s one that has been overlooked more recently because the power demands of modern devices have outstripped traditional solar panels’ capacity.

“It’s power density,” Vivian Qu, co-founder and CEO of RadianX, told TechCrunch. “The reason why perovskites have been so interesting is the high power density”

Perovskites are also not a new idea, though the class of materials has struggled to gain a foothold. They’re still more expensive than typical silicon-based solar panels, and they’re not quite as durable, though they’ve made strides in recent years.

But they make up for those shortcomings in power delivery — RadianX’s 1.2 meter by 0.6 meter panel, for example, harvests light with 22.33% efficiency, which the company said is the best on record.

For RadianX, durability is also less of a concern. The company has been able to hit a key industry standard for durability, and by targeting indoor devices, the company’s panels are subject to less wear-and-tear. The panels, which can be as thin as 0.7 millimeters, can be sized to fit.

To wring more power out of the panels, RadianX is also developing power electronics tailored to perovskites. Most existing electronics are tuned for silicon panels, but “silicon has a very different light soaking characteristic,” she said.

Unlike many other solar companies, RadianX isn’t planning to sell bare panels. “RadianX is trying to package all of this and sell this to device makers as something they don’t need to worry about,” Qu said.

Ultimately, Qu and Douglas hope their power packages will land in everything from e-readers to factory sensors — and maybe a few places they haven’t dreamt of yet.